[ICS 6 + FTP] Why does server accept two files with same filename?

Hello

    I used ICS 6 to update a file on a web server through its FTP
server, and noticed that if I just upload the file without deleting
the existing copy beforehand, the server happily keeps two copies of
the same file!

==========
    FtpClient1.UserName:='mylogin';
    FtpClient1.PassWord:='mypasst';
    FtpClient1.HostName:='ftp.acme.com';
    FtpClient1.Passive := True;
    FtpClient1.LocalFileName:='.\myfile.txt';
    FtpClient1.HostDirName:='/';
    FtpClient1.HostFileName := FtpClient1.LocalFileName;
    try
      FtpClient1.Connect;
      FTPClient1.Binary := True;
      FtpClient1.Put;
      FtpClient1.Quit;
    except
      Memo1.Lines.Add('Error uploading to FTP. Disconnecting.');
      Button1.Enabled := True;
      Button1.Caption := OrigText;
    end;
    Memo1.Lines.Add('FTP Done');
==========

How can a (Unix) FTP server host more than one copy of the exact same
filename in the same directory?

Thank you?